User instructions are application-specific and can perform operations listed in Handling Instruction Invocation. The instruction class set of a node contains instruction classes for user and mixed-type instructions an assembler program loaded into the node can contain. To find an instruction class for a user instruction, the assembler converts its parameters to canonical form according to the rules described in Setting Text Instruction Parameters.
You can split the parameters of a user instruction into multiple lines at positions of commas located outside of string literals. To indicate a continuation of instruction parameters on the next line, finish the previous line just after a comma following an instruction parameter.